Modified atmosphere package

ABSTRACT

A modified atmosphere packaging method creates a modified atmosphere in a package including an inner package and an outer package. The inner package is composed at least partially of a polymeric material substantially permeable to oxygen, while the outer package is composed of a polymeric material substantially impermeable to oxygen. After a food product such as raw meat is placed within the inner package, the inner package is flushed with a desired mixture of gases to substantially remove oxygen from the inner package. The flushed inner package is then sealed and inserted into the outer package without sealing the outer package. Next, the outer package is flushed with the desired mixture of gases to substantially remove oxygen from the outer package. After flushing the outer package, the outer package is sealed. An oxygen scavenger is provided in the package to substantially absorb any residual oxygen within the package. The oxygen scavenger is activated with an oxygen uptake accelerator to increase the rate at which the residual oxygen is absorbed.

This is a continuation of application Ser. No. 08/763,719 filed Dec. 13,1996, now U.S. Pat. No. 5,811,142, which is a continuation-in-part ofU.S. patent application Ser. No. 08/627,137 filed Apr. 3, 1996 now U.S.Pat. No. 5,698,250.

FIELD OF THE INVENTION

The present invention relates generally to modified atmosphere packagesfor storing food. More particularly, the invention relates to a modifiedatmosphere package for extending the shelf life of raw meats or otherfood.

BACKGROUND OF THE INVENTION

Containers have long been employed to store and transfer perishable foodprior to presenting the food at a market where it will be purchased bythe consumer. After perishable foods, such as meats, fruits, andvegetables, are harvested, they are placed into containers to preservethose foods for as long as possible. Maximizing the time in which thefood remains preserved in the containers increases the profitability ofall entities in the chain of distribution by minimizing the amount ofspoilage.

The environment around which the food is preserved is a critical factorin the preservation process. Not only is maintaining an adequatetemperature important, but the molecular and chemical content of thegases surrounding the food is significant as well. By providing anappropriate gas content to the environment surrounding the food, thefood can be better preserved when maintained at the proper temperatureor even when it is exposed to variations in temperature. This gives thefood producer some assurance that after the food leaves his or hercontrol, the food will be in an acceptable condition when it reaches theconsumer.

Modified atmosphere packaging systems for one type of food, raw meats,exposes these raw meats to either extremely high levels or extremely lowlevels of oxygen (O₂). Packaging systems which provide extremely lowlevels of oxygen are generally preferable because it is well known thatthe fresh quality of meat can be preserved longer under anaerobicconditions than under aerobic conditions. Maintaining low levels ofoxygen minimizes the growth and multiplication of aerobic bacteria.Heretofore, low-level oxygen systems, such as the systems proposed inU.S. Pat. No. 3,574,642 to Weinke and U.S. Pat. No. 5,115,624 toGarwood, have obtained extremely low levels of oxygen by relying uponoxygen evacuation techniques.

In typical prior art packaging systems, a package composed of flexibleor rigid gas barrier materials is loaded into an evacuation chamber. Thepackage in the evacuation chamber is subjected to a vacuum which removesas much of the gases surrounding the package as possible. At this pointthe package is sealed. After the evacuated package is sealed, the rawmeat either can be maintained in a "zero" atmosphere environment(commonly referred to as vacuum packaging) or can be refilled with a gasor mixture of gases to provide a modified atmosphere environment. Toprovide a modified atmosphere environment, the air-evacuated package istypically filled with a mixture of gases consisting of about 30 percentcarbon dioxide (CO₂) and 70 percent nitrogen (N₂). Refilling theair-evacuated package with such a mixture of gases is believed tosuppress the growth of anaerobic bacteria. The meat in the modifiedatmosphere package takes on a less desirable purple-red color which fewconsumers would associate with freshness. This purple-red color,however, quickly "blooms" to a bright red color generally associatedwith freshness when the package is opened to oxygenate the fresh meat byexposure to air. The package is typically opened immediately prior todisplay of the fresh meat to consumers so as to induce blooming of thefresh meat just prior to display to the consumers.

Low-level oxygen systems relying upon evacuation techniques to diminishoxygen levels suffer from several disadvantages. For example, suchsystems operate at exceptionally slow speeds because they require theuse of an evacuation device along the packaging line. The evacuationprocess is time-consuming. Typically, only about four to six evacuatedpackages can be prepared on a packaging line in one minute. In addition,the evacuation techniques render it difficult to remove any oxygenwithin a previously wrapped package such as an overwrapped meat tray.The trapped oxygen raises the residual oxygen level in the package andcan also cause billowing and subsequent damage to the package duringevacuation.

A need therefore exists for a modified atmosphere package and a systemfor making that package which overcome the aforementioned shortcomingsassociated with existing modified atmosphere packages and existingsystems for making those packages.

SUMMARY OF THE INVENTION

Briefly, the present invention is directed to a new and improvedmodified atmosphere package for extending the shelf life of food,especially raw meats. Moreover, the present invention is directed to anew and improved modified atmosphere packaging system for producing theforegoing packages which operates at significantly higher speeds thanprior art systems and which reduces the oxygen level in the packageswithout the use of time-consuming evacuation techniques. The packagingsystem effectively extends the allowable time period between cutting andpurchase of retail cuts of raw meat. The raw meat can be cut andpackaged several weeks prior to being purchased at the store and yetremains fresh during this time period.

The modified atmosphere package maintains an appropriate containedatmosphere around food being contained therein when stored in an ambientenvironment. A modified atmosphere packaging system and method creates amodified atmosphere in the package. In one embodiment, the modifiedatmosphere package includes an inner package and an outer package. Theinner package is composed at least partially of a polymeric materialsubstantially permeable to oxygen, while the outer package is composedof a polymeric material substantially impermeable to oxygen. After afood product such as raw meat is placed within the inner package, theinner package may be flushed with a desired mixture of gases tosubstantially remove oxygen from the inner package. The flushed innerpackage is then wrapped and inserted into the outer package withoutsealing the outer package. Next, the outer package is flushed with thedesired mixture of gases to substantially remove oxygen from the outerpackage. After flushing the outer package, the outer package is sealed.An oxygen scavenger is provided in the modified atmosphere package tosubstantially absorb any residual oxygen within the package. The oxygenscavenger is preferably activated with an oxygen uptake accelerator toincrease the rate at which the residual oxygen is absorbed.

The above summary of the present invention is not intended to representeach embodiment, or every aspect of the present invention. This is thepurpose of the Figures and detailed description which follow.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to thedrawings in which:

FIG. 1 is an isometric view of a modified atmosphere package embodyingthe present invention;

FIG. 2 is a section view taken generally along line 2--2 in FIG. 1;

FIG. 3 is an enlarged view taken generally along circled portion 3 inFIG. 2;

FIG. 4 is a diagrammatic side view of a system for making the modifiedatmosphere package in FIG. 1;

FIG. 5 is an elevational view of an alternative embodiment of a modifiedatmosphere package.

While the invention is susceptible to various modifications andalternative forms, certain specific embodiments thereof have been shownby way of example in the drawings and will be described in detail. Itshould be understood, however, that the intention is not to limit theinvention to the particular forms described. On the contrary, theintention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theappended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to the drawings, FIGS. 1-3 depict a modified atmospherepackage 10 including an outer package 12 and an inner package 14. Theterm "package " as used herein shall be defined as any means for holdingraw meat, including a container, carton, casing, parcel, holder, tray,flat, bag, film envelope, etc. At least a portion of the inner package14 is permeable to oxygen. The inner package 14 includes a conventionalsemi-rigid plastic tray 16 thermoformed from a sheet of polymericmaterial which is substantially permeable to oxygen. Exemplary polymerswhich may be used to form the non-barrier tray 16 include polystyrenefoam, cellulose pulp, polyethylene, polypropylene, etc. In a preferredembodiment, the polymeric sheet used to form the tray 16 issubstantially composed of polystyrene foam and has a thickness rangingfrom about 100 mils to about 300 mils. The use of a common polystyrenefoam tray 16 is desirable because it has a high consumer acceptance. Theinner package 14 further includes a stretch film wrapping or cover 18substantially composed of a polymeric material, such as polyvinylchloride (PVC), which is substantially permeable to oxygen. In apreferred embodiment, the stretch film used to form the cover 18contains additives which allow the film to cling to itself, has athickness ranging from about 0.5 mil to about 1.5 mils, and has a rateof oxygen permeability greater than about 1000 cubic centimeters per 100square inches in 24 hours. Most preferably, the film has a rate ofoxygen permeability grater than about 10,000 cubic centimeters per 100square inches in 24 hours. To help attain this high rate ofpermeability, small holes may be punched into the film. One preferredstretch film is Resinite™ meat film commercially available from BordenPackaging and Industrial Products of North Andover, Mass.

The tray 16 is generally rectangular in configuration and includes abottom wall 20, a continuous side wall 22, and a continuous rim orflange 24. The continuous side wall 22 encompasses the bottom wall 20and extends upwardly and outwardly from the bottom wall 20. Thecontinuous rim 24 encompasses an upper edge of the continuous side wall22 and projects laterally outwardly therefrom. A food item such as aretail cut of raw meat 26 is located in a rectangular compartmentdefined by the bottom wall 20 and continuous side wall 22. The raw meatmay be any animal protein, including beef, pork, veal, lamb, chicken,turkey, venison, fish, etc. Prior to fully wrapping the tray 16 with thecover 18, the partially formed inner package 14 may be flushed with anappropriate mixture of gases, typically a mixture of about 30 percentcarbon dioxide and about 70 percent nitrogen, to lower the oxygen levelin the inner package 14 to about 1.5 to 5.0 percent. The foregoingmixture of gases displaces the oxygen within the inner package 14 duringthe flushing operation. After flushing the inner package 14, the tray 16is manually or automatically wrapped with the cover 18. The cover 18 iswrapped over the retail cut of raw meat 26 and about both the side wall22 and bottom wall 20 of the tray 16. The free ends of the cover 18 areoverlapped along the underside of the bottom wall 20 of the tray 16,and, due to the cling characteristic inherent in the cover 18, theseoverlapping free ends cling to one another to hold the cover 18 inplace. If desired, the overwrapped tray 16, i.e., the inner package 14,may be run over a hot plate to thermally fuse the free ends of the cover18 to one another and thereby prevent these free ends from potentiallyunraveling.

The outer package 12 is preferably a flexible polymeric bag composed ofa single or multilayer plastics material which is substantiallyimpermeable to oxygen. The polymeric bag 12 may, for example, include amultilayer coextruded film containing ethylene vinyl chloride (EVOH), orinclude an oriented polypropylene (OPP) core coated with an oxygenbarrier coating such as polyvinylidene chloride and further laminatedwith a layer of sealant material such as polyethylene to facilitate heatsealing. In a preferred embodiment, the polymeric bag 12 is composed ofa coextruded barrier film commercially available as product no.325C44-EX861B from PrintPack, Inc. of Atlanta, Ga. The coextrudedbarrier film has a thickness ranging from about 2 mils to about 6 mils,and has a rate of oxygen permeability less than about 0.1 cubiccentimeters per 100 square inches in 24 hours. Prior to sealing theperipheral edges of the polymeric bag 12, the inner package 14 is placedwithin the polymeric bag 12. Also, the bag 12 is flushed with anappropriate mixture of gases, typically about 30 percent carbon dioxideand about 70 percent nitrogen, to lower the oxygen level in the bag 12to about 0.05 to 5.0 percent. After flushing the bag 12, but still priorto sealing the bag 12, an oxygen scavenger/absorber 28 is placed in thebag 12 external to the sealed inner package 14. The bag 12 is thensealed.

The oxygen scavenger 28 is designed to reduce the oxygen level in thebag 12 at a rate sufficient to prevent discoloration (e.g., browning) ofthe raw meat 26. Many factors influence the color stability of raw meat,but it has been found that the reduction of the oxygen level from the0.05 to 5.0 percent level described about to less than about 0.05percent within 90 minutes works for all types of raw meat. If there isstill oxygen in the bag 12 after this time period, the oxygen scavenger28 absorbs any remaining oxygen in the bag 12 and any oxygen which mightstill be trapped within the inner container 14 so as to lower the oxygenlevel in the bag 12 to about zero percent within 24 hours. The oxygenscavenger 28 also absorbs any oxygen which might permeate into the bag12 from the ambient environment. To increase the rate of oxygenabsorption, the oxygen scavenger is activated with an oxygen uptakeaccelerator in the form of a predetermined amount of activating agent orby other means just prior to being placed in the bag 12. The oxygenuptake accelerator is preferably selected from the group consisting ofwater or aqueous solutions of acetic acid, citric acid, sodium chloride,calcium chloride, magnesium chloride and copper.

Further information concerning the oxygen scavenger 28, the oxygenuptake accelerator, and the means for introducing the oxygen uptakeaccelerator to the oxygen scavenger 28 may be obtained from applicationSer. No. 08/700,644, filed Aug. 8, 1996, and now abandoned, entitled"Oxygen Scavenger Accelerator," and incorporated herein by reference. InFIGS. 1-3, the oxygen scavenger 28 is illustrated as a packet or labelwhich is inserted into the bag 12 prior to sealing the bag 12.Alternatively, an oxygen scavenging material may be added to the polymeror polymers used to form the outer package 12 so that the oxygenscavenging material is integrated into the outer package 12 itself.

The retail cut of raw meat 26 within the modified atmosphere package 10takes on a purple-red color when the oxygen is removed from the interiorof the package 10. The meat-filled modified atmosphere package 10 maynow stored in a refrigeration unit for several weeks prior to beingoffered for sale at a grocery store. A short time (e.g., less than onehour) prior to being displayed at the grocery store, the inner package14 is removed from the polymeric bag 12 to allow oxygen from the ambientenvironment to permeate the non-barrier tray 16 and non-barrier cover18. The purple-red color of the raw meat 26 quickly changes or "blooms"to a generally acceptable bright red color when the raw meat 26 isoxygenated by exposure to air.

FIG. 4 illustrates a modified atmosphere packaging system used toproduce the modified atmosphere package 10 in FIGS. 1-3. The packagingsystem integrates several disparate and commercially availabletechnologies to provide a modified atmosphere for retail cuts of rawmeat. The basic operations performed by the packaging system aredescribed below in connection with FIG. 4.

The packaging process begins at a thermoforming station 30 where a tray16 is thermoformed in conventional fashion from a sheet of polystyreneor other non-barrier polymer using conventional thermoforming equipment.The thermoforning equipment typically includes a male die member 30a anda female die cavity 30b. As is well known in the thermoforming art, thetray 16 is thermoformed by inserting the male die member 30a into thefemale die cavity 30b with the polymeric sheet disposed therebetween.

The thermoformed tray 16 proceeds to a goods loading station 32 wherethe tray 16 is filled with a food product such as a retail cut of rawmeat 26. The meat-filled tray 16 is then manually carried or transportedon a conveyor 34 to a conventional stretch wrapping station 36 where astretch film 18 is wrapped about the tray 16 to enclose the retail cutof meat 26 therein. The overwrapped tray 16 forms the inner package 14.Just prior to sealing the meat-filled tray 16 at the stretch wrappingstation 36, the tray 16 is flushed with a mixture of carbon dioxide andnitrogen to reduce the oxygen level in the tray 16 to about 1.5 to 5.0percent. The mixture of carbon dioxide and nitrogen emanates from aconventional gas supply hollow tube or rod 40 fed by a gas tank (notshown). The stretch wrapping station 36 may be implemented with acompact stretch semi-automatic wrapper commercially available fromHobart Corporation of Troy, Ohio.

Next, the flushed and sealed inner package 14 proceeds to a high speedform, fill, and seal station 42 which may be implemented with aFuji-Formost high-speed horizontal form-fill-seal machine commerciallyavailable as model no. FW-3700 from Formost Packaging Machines, Inc. ofWoodinville, Wash. The inner package 14 may be transported to the form,fill, and seal station 42 by a conveyor 44. At the form, fill, and sealstation 42, a web 46 of oxygen barrier film from a roll 47 is arrangedto run along the direction of movement of the inner package 14. The web46 of film is fed to a conventional forming box which forms a section 48of the web 46 into a tube configuration encompassing the inner package14. The tube-shaped section 48 of the web 46 is thermally sealed along alower fin 50 and is thermally sealed at one end 52 by a pair ofvertically-oscillating heated sealing bars 54 or the like.

Just prior to sealing the other end 56 of the tube-shaped web section 48to complete formation of the polymeric bag 12, the web section 48 isflushed with an appropriate mixture of gases, typically about 30 percentcarbon dioxide and about 70 percent nitrogen, to lower the oxygen levelin the bag 12 to about 0.05 to 5.0 percent. The mixture of carbondioxide and nitrogen emanates from a conventional gas supply hollow tubeor rod 58 fed by a gas tank (not shown). After flushing the web section48, but still prior to sealing the end 56, the oxygen scavenger/absorber28 is placed in the web section 48 external to the sealed innercontainer 14 and the oxygen scavenger 28 is activated with an oxygenuptake accelerator. The end 56 is then conveyed between and sealed bythe heated sealing bars 54 to complete formation of the bag 12. Inaddition to thermally fusing the web section 48 at the end 56, theheated sealing bars 54 sever the web section 48 at the end 56 toseparate the bag 12 from the next upstream web section being formed intoanother bag. The sealed bag 12 is substantially in the form of a sealedbubble or envelope loosely containing the inner package 14 and providinga sealed modified atmosphere surrounding the inner package 14.

The oxygen scavenger 28 lowers the oxygen level in the package 10 fromthe previously described 0.05 to 5.0 percent oxygen level to less thanabout 0.05 percent within a time period of about 90 minutes. Althoughthe oxygen scavenger 28 is depicted in FIG. 4 as a packet or labelinserted into the polymeric bag 12, an oxygen scavenger mayalternatively be integrated into the polymers used to form the bag 12.One preferred oxygen scavenger is a FreshPax™ oxygen absorbing packetcommercially available from MultiSorb Technologies, Inc. (formerlyMultiform Desiccants Inc.) of Buffalo, N.Y.

The modified atmosphere packaging system in FIG. 4 can produce themodified atmosphere packages 10 at cycle rates ranging from about 1 to60 packages per minute. The maximum cycle rates which can be attained bythe system in FIG. 4 are significantly higher than the cycle rates whichcan be achieved by prior art systems. The attainment of high cycle ratesis largely due to the fact that the packaging system in FIG. 4 reliesupon the use of simple, commercially available, and high-speed form,fill, and seal equipment, as opposed to the slower evacuation equipmentemployed by prior art systems. Reducing oxygen levels in the modifiedatmosphere package 10 by first flushing the package 10 and thensubsequently introducing the activated oxygen scavenger 28 into thepackage 10 is significantly faster and more cost-effective than thereliance upon slow evacuation techniques.

While the present invention has been described with reference to one ormore particular embodiments, those skilled in the art will recognizethat many changes may be made thereto without departing from the spiritand scope of the present invention. For example, as shown in FIG. 5,multiple inner packages 14 may be placed into a single outer package 12.Each of these embodiments and obvious variations thereof is contemplatedas falling within the spirit and scope of the claimed invention, whichis set forth in the following claims.

What is claimed is:
 1. A modified atmosphere package comprising firstand second compartments separated by a partition member, said partitionmember including a non-barrier portion substantially permeable tooxygen, said first and second compartments being encompassed by an outerwall substantially impermeable to oxygen, said first compartment beingsubstantially free of oxygen in response to substantially removing theoxygen from said pocket and introducing one or more gases creating amodified atmosphere within said first compartment, said firstcompartment containing an oxygen scavenger activated with an oxygenscavenger accelerator to substantially absorb residual oxygen withinsaid first compartment, said second compartment containing a retail cutof raw meat.
 2. The package of claim 1, wherein said partition memberincludes a tray covered by a stretch film wrapping, said tray and saidstretch film wrapping enclosing said second compartment.
 3. The packageof claim 1, wherein said non-barrier portion of said partition memberhas a rate of oxygen permeability greater than about 1000 cubiccentimeters per 100 square inches in 24 hours.
 4. The package of claim3, wherein said outer wall has a rate of oxygen permeability less thanabout 0.1 cubic centimeters per 100 square inches in 24 hours.
 5. Thepackage of claim 1, wherein said oxygen scavenger is constructed toreduce a level of said residual oxygen to less than about 0.05 percentwithin 90 minutes after flushing said first compartment.
 6. The packageof claim 1, wherein said oxygen scavenger includes an oxygen-absorbingpacket disposed within said first compartment.
 7. The package of claim1, wherein said oxygen scavenger includes an oxygen-absorbing materialintegrated into the material used to form said partition member.
 8. Thepackage of claim 1, wherein said outer wall includes a plastic bag. 9.The package of claim 1, wherein said retail cut of raw meat issubstantially totally enclosed within said second compartment.
 10. Amethod of manufacturing a modified atmosphere package having first andsecond compartments separated by a partition member, said partitionmember including a non-barrier portion substantially permeable tooxygen, said first and second compartments being encompassed by an outerwall substantially impermeable to oxygen, said method comprising thesteps of:placing a retail cut of raw meat within said secondcompartment; sealing said second compartment; substantially removingoxygen from said first compartment and introducing one or more gases;supplying said first compartment with an oxygen scavenger to absorbresidual oxygen within said first compartment; activating said oxygenscavenger with an oxygen scavenger accelerator; and sealing said outerwall.
 11. The method of claim 10, wherein said partition member includesa tray covered by a stretch film wrapping, said tray and said stretchfilm wrapping enclosing said second compartment.
 12. The method of claim11, wherein said outer wall includes a plastic bag.
 13. The method ofclaim 10, wherein said non-barrier portion of said partition member hasa rate of oxygen permeability greater than about 1000 cubic centimetersper 100 square inches in 24 hours.
 14. The method of claim 13, whereinsaid outer wall has a rate of oxygen permeability less than about 0.1cubic centimeters per 100 square inches in 24 hours.
 15. The method ofclaim 10, wherein said oxygen scavenger is constructed to reduce a levelof said residual oxygen to less than about 0.05 percent within 90minutes after flushing said first compartment.
 16. A modified atmospherepackage, comprising:a first package configured and sized tosubstantially totally enclose a retail cut of raw meat and including anon-barrier portion substantially permeable to oxygen; a second packagecovering said first package and being substantially impermeable tooxygen, said second package creating a pocket between said first packageand said second package, said pocket being substantially free of oxygenin response to substantially removing the oxygen from said pocket andintroducing one or more gases creating a modified atmosphere within saidpocket; and an oxygen scavenger positioned external to said firstpackage to substantially absorb residual oxygen within said pocket, saidoxygen scavenger being activated with an oxygen uptake accelerator. 17.A method of manufacturing a modified atmosphere package, said methodcomprising the steps of:supplying a first package including anon-barrier portion substantially permeable to oxygen; placing a retailcut of raw meat within said first package; sealing said first package;supplying a second package substantially impermeable to oxygen; coveringsaid first package with said second package without sealing said secondpackage so as to create a pocket between said first package and saidsecond package; substantially removing oxygen from said pocket andintroducing one or more gases into said pocket to create a modifiedatmosphere therein; supplying an oxygen scavenger positioned external tosaid first package to absorb residual oxygen within said pocket;activating said oxygen scavenger with an oxygen scavenger accelerator;and sealing said second package.